Conventional can-annular gas turbine engines include a plurality of individual combustor cans, where each can is secured to a respective transition duct that directs combustion gases from the combustor can, and through inlet guide vanes to a respective portion of a turbine inlet annulus. Each flow of combustion gas remains discrete from the combustor until exiting the respective transition duct. In contrast, in certain emerging gas turbine engines that use can combustors, the array of transition ducts are replaced with a duct arrangement that receives the discrete combustion gas flows from repositioned combustor cans, accelerates them to a speed appropriate for delivery onto the first row of turbine blades, and directs them into a common duct structure that may include an annular chamber where the combustion gas flows are no longer segregated from each other. The annular chamber exhausts directly into the turbine inlet. (Other configurations exist where the individual flows remain discrete even within the common duct structure.) The proper orientation and speed created by the arrangement eliminates the need for a first row of inlet guide vanes present in the conventional arrangements. An example of this configuraton may be seen in US Patent Application Publication Number 2011/0203282 to Charron et al., published Aug. 25, 2011, which is incorporated by reference in its entirety herein.
In conventional gas turbine engine combustor arrangements, since the combustion gas flows are not accelerated a substantial amount in the transition ducts there is a relatively small static pressure difference between compressed air in the plenum surrounding the transition duct and a static pressure of the combustion gas flows within the transition. Consequently, there is a relatively small force pressing inward on the exterior surface of the transition ducts.
In contrast, in the emerging technology ducting arrangement the combustion gas flows are traveling at significantly greater speeds. This results in significantly greater pressure differences (up to six atmospheres) and resulting forces acting on the exterior surface of the ducting arrangement. In configurations with an accelerating geometry that accelerates the combustion gas flows to the proper speed for delivery onto the first row of turbine blades, such as the configuration with the annular chamber, the annular chamber experiences the greatest of these forces because the combustion gas flows are fully accelerated when in the annular chamber. These forces act to deform the ducting arrangement, in particular the annular chamber, and there is room in the art for improvements that resist this deformation.